This is not correct. The field is actually 288 bits (v4 uses 144 bits). Some of these bits are used for protocol, flags and such, 2 bits are used for IPv6 address type. The remaining available for IPv6 addresses + ports is 256. Source and destination are each allotted 128 bits. The bits removed are [39:24] ie. 3333:3333:3333:3333:3333:33xx:xx33:AAAA in the OP example. The part marked x is removed.
See the following for specifics: http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SXF/native/configuration/guide/acl.html#wp1090842 Embedded IPv4 removes the upper 16 bits as these are all zero. Link local discard bits 95:80 which are zero. All other formats remove bits [39:24] The misunderstanding is anything with a prefix longer than /88 includes discarded bits in the subnet portion as opposed to the host portion. Mack McBride Network Architect -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Saku Ytti Sent: Wednesday, December 08, 2010 1:38 PM To: [email protected] Subject: Re: [c-nsp] "Compressed" IPv6 ACLs on Cat6500 > Where did you arrive to 112? My understanding of the compressed mode is > 128-src_port-dst_port-flags = 128-16-16 = 88 usable bits for addresses. omitted -8 there, flags = 8bits, so 128-16-16-8 = 88. -- ++ytti _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/ _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
